1. Field of the Invention
The present invention relates generally to a vehicle door latch device, and more particularly to a vehicle door latch device with a block type anti-theft mechanism.
2. Prior Art
A conventional door latch device includes a lock lever which is displaceable, by unlocking and locking operations of an inside lock button of the door, between an unlocked position where it makes a door-opening operation of the outside open handle effective and a locked position where it makes the door-opening operation of the outside open handle ineffective. Because the inside lock button to which the lock lever should be connected is exposed on an interior surface of the door, the lock button does not have so high an anti-theft performance. For example, it is very easy to operate the lock button by breaking a door glass from outside the vehicle to illegally change the lock lever to the unlocked position. To invalidate such an illegal access to the lock button, a number of anti-theft mechanisms have been developed.
The anti-theft mechanism is classified to two types depending on its structure. One of them is a type containing a free-play mechanism provided between the inside lock button and the lock lever. The free-play mechanism can absorb an unlocking movement of the lock button so as not to transmit the unlocking movement to the lock lever. That is, no force is applied to the lock lever even if the lock button is operated to unlock. This free-play mechanism effectively invalidates the illegal access to the inside lock button. However, the free-play type anti-theft mechanism is not capable of preventing an illegal access to the lock lever by means of a special tool which is inserted into a gap between a door frame and a door glass. That is, although the free-play type anti-theft mechanism is capable of improving anti-theft performance of the inside lock button, it is not capable of improving the anti-theft performance of the lock lever.
Another anti-theft mechanism is a type having a block member which makes the lock lever immovable. The block member comes into contact with the lock lever mechanically so as to restrict a displacement of the lock lever from the locked position to the unlocked position. This block type anti-theft mechanism is capable of improving both the anti-theft performances of the lock lever and the lock button.
The above-mentioned block type anti-theft mechanism has some disadvantages. A first disadvantages is that the block member is not protected from the illegal access. Thus, after the mechanical contact between the block member and the lock lever is released by a first illegal access against the block member, the lock lever may be offended by a second illegal access.
A second disadvantage is that the block type anti-theft mechanism requires the door latch device to have a high strength. Because, in the block type anti-theft mechanism, an external force applied to the inside lock button by the illegal access is transmitted to the lock lever, the components such as a lock lever, lock button, and block member must have a strength resisting the external force generated by the powerful illegal access. This increases weight and size of components.
A third disadvantage is that the block type anti-theft mechanism does not go well with the well known one-motion door opening mechanism which carries out restoration of the lock lever from the locked position to the unlocked position and opening of the door substantially at the same time, by an opening operation of an inside open handle of the door. The door latch device with the one-motion door opening mechanism transmits an opening movement of the inside open handle to the lock lever located at the locked position in order to displace the lock lever to the unlocked position. However, because the block type anti-theft mechanism is a mechanism for restricting the displacement of the lock lever from the locked position to the unlocked position, a large load is applied to parts such as the lock lever and block member if the opening movement of the inside open handle is transmitted to the lock lever through the one-motion door opening mechanism. Therefore, according to the prior art device, when the block type anti-theft mechanism and the one-motion door opening mechanism are installed in the latch device at the same time, a sufficient strength needs to be secured for the above-mentioned parts not to be deformed by a strong operating force of the inside open handle.
Accordingly, an object of the present invention is to provide a vehicle door latch device with the block type anti-theft mechanism which overcomes the above-mentioned disadvantages.